Ethylbenzene column

In the Mohil-Badger vapor-phase process, fresh and recycled benzene are vaporized and preheated to the desired temperature and fed to a multistage fixed-bed reactor. Ethylene is distributed to the individual stages. Alkylation takes place in tile vapor phase. Separately, file polyethylbenzene stream from the distillation section is mixed with benzene, vaporized and heated, and fed to the transalkylator, where polyethylbenzenes react with benzene to form additional ethylbenzene. The combined reactor effluent is distilled in the benzene column. Benzene is condensed in the overhead for recycle to the reactors. The bottoms from the benzene column are distilled in the ethylbenzene column to recover the ethylbenzene product in the overhead. The bottoms stream from the ethylbenzene column is further distilled in the polyefitylbenzene column to remove a small quantity of residue. The overhead polyethylbenzene stream is recycled to the reactor section for transalkylation to ethylbenzene. 

Extractor 2 Decomposer 3 Isomerization column 4 Heavy ends colunm 5 Raffinatestripping colunm 6 Light ends column 7 Ethylbenzene column 8 o-Xylene colunm... 

Alkylation reactors 2 Prefractionation column 3 Benzene column 4 Ethylbenzene column 5 Column for polyalkylated benzenes 6 Waste-gas scrubber... 

Ethylbenzene column 2 Light ends column 3 Benzene/toluene column 4 Styrene column... 

Ethylbenzene Separation. Ethylbenzene [100-41-4] which is primarily used in the production of styrene, is difficult to separate from mixed Cg aromatics by fractionation. A column of about 350 trays operated at a refluxTeed ratio of 20 is required. No commercial adsorptive unit to accomplish this separation has yet been installed, but the operation has been performed successhiUy in pilot plants (see Table 5). About 99% of the ethylbenzene in the feed was recovered at a purity of 99.7%. This operation, the UOP Ebex process, requires about 40% of the energy that is required by fractional distillation. 

Fig. 3. Unocal—Lummus—UOP ethylbenzene process AR = alkylation reactor TR = transalkylation reactor BC = benzene column ...

Eig. 4. Mobil—Badger process for ethylbenzene production H = heater Rx = reactor P = prefractionator BC = benzene recovery column ... 

VS = vent gas scrubber EC = ethylbenzene recovery column DC = diethylbenzene recovery column. 

Figure 5 illustrates a typical distillation train in a styrene plant. Benzene and toluene by-products are recovered in the overhead of the benzene—toluene column. The bottoms from the benzene—toluene column are distilled in the ethylbenzene recycle column, where the separation of ethylbenzene and styrene is effected. The ethylbenzene, containing up to 3% styrene, is taken overhead and recycled to the dehydrogenation section. The bottoms, which contain styrene, by-products heavier than styrene, polymers, inhibitor, and up to 1000 ppm ethylbenzene, are pumped to the styrene finishing column. The overhead product from this column is purified styrene. The bottoms are further processed in a residue-finishing system to recover additional styrene from the residue, which consists of heavy by-products, polymers, and inhibitor. The residue is used as fuel. The residue-finishing system can be a flash evaporator or a small distillation column. This distillation sequence is used in the Fina-Badger process and the Dow process. 

Fig. 5. Purification of styrene in the dehydrogenation reactor effluent in the FinaBadger styrene process A, ben2ene—toluene column B, ethylbenzene recycle column C, styrene finishing column and D, residue finishing. Courtesy of The Badger Company, Inc.

One of the early column crystallizers was that iatroduced for the separation of xylene isomers (see Xylene and Ethylbenzene). In this unit, shown schematically ia Eigure 25, -xylene crystals are formed ia a scraped-surface chiller above the column and fed to the column. The crystals move downward counter-currenfly to impure Hquid ia the upper portion of the column and melted -xylene ia the lower part of the column. Impure Hquor is withdrawn from an appropriate poiat near the top of the column of crystals while pure product, xylene, is removed from the bottom of the column. The pulse unit drives melt up the column as reflux and iato a product receiver. 

There are notable cases where plate columns have been converted to packed columns to gain advantage of the low pressure drop exacted from the vapor stream. More recently the packings have been largely of the stmctured type. Illustrative of this is the trend toward the use of stmctured packing in ethylbenzene—styrene fractionators, some of which have diameters of 10 m or higher. 

The absolute pressure may have a significant effect on the vapor—Hquid equiHbrium. Generally, the lower the absolute pressure the more favorable the equiHbrium. This effect has been discussed for the styrene—ethylbenzene system (30). In a given column, increasing the pressure can increase the column capacity by increasing the capacity parameter (see eqs. 42 and 43). Selection of the economic pressure can be faciHtated by guidelines (89) that take into consideration the pressure effects on capacity and relative volatiHty. Low pressures are required for distillation involving heat-sensitive material. 

Example 8 Calculation of Rate-Based Distillation The separation of 655 lb mol/h of a bubble-point mixture of 16 mol % toluene, 9.5 mol % methanol, 53.3 mol % styrene, and 21.2 mol % ethylbenzene is to be earned out in a 9.84-ft diameter sieve-tray column having 40 sieve trays with 2-inch high weirs and on 24-inch tray spacing. The column is equipped with a total condenser and a partial reboiler. The feed wiU enter the column on the 21st tray from the top, where the column pressure will be 93 kPa, The bottom-tray pressure is 101 kPa and the top-tray pressure is 86 kPa. The distillate rate wiU be set at 167 lb mol/h in an attempt to obtain a sharp separation between toluene-methanol, which will tend to accumulate in the distillate, and styrene and ethylbenzene. A reflux ratio of 4.8 wiU be used. Plug flow of vapor and complete mixing of liquid wiU be assumed on each tray. K values will be computed from the UNIFAC activity-coefficient method and the Chan-Fair correlation will be used to estimate mass-transfer coefficients. Predict, with a rate-based model, the separation that will be achieved and back-calciilate from the computed tray compositions, the component vapor-phase Miirphree-tray efficiencies. 

Billet and cowodcers [Chem. Jng. Tech., 38, 825 (1966) Jnstn. Chem. Engrs. Symp. Set No. 32, 5, 111 (1969] used the ethylbenzene/ styrene system at 100 torr and a 0.8-m column with 500-mm plate spacing. Two weir heights were used, 19 and 38 mm. Operation was at... 

The dehydrogenation reaction produces crude styrene which consists of approximately 37.0% styrene, 61% ethylbenzene and about 2% of aromatic hydrocarbon such as benzene and toluene with some tarry matter. The purification of the styrene is made rather difficult by the fact that the boiling point of styrene (145.2°C) is only 9°C higher than that of ethylbenzene and because of the strong tendency of styrene to polymerise at elevated temperatures. To achieve a successful distillation it is therefore necessary to provide suitable inhibitors for the styrene, to distil under a partial vacuum and to make use of specially designed distillation columns. 

FIGURE l.l Hydrophobic interaction and reversed-phase chromatography (HIC-RPC). Two-dimensional separation of proteins and alkylbenzenes in consecutive HIC and RPC modes. Column 100 X 8 mm i.d. HIC mobile phase, gradient decreasing from 1.7 to 0 mol/liter ammonium sulfate in 0.02 mol/liter phosphate buffer solution (pH 7) in 15 min. RPC mobile phase, 0.02 mol/liter phosphate buffer solution (pH 7) acetonitrile (65 35 vol/vol) flow rate, I ml/min UV detection 254 nm. Peaks (I) cytochrome c, (2) ribonuclease A, (3) conalbumin, (4) lysozyme, (5) soybean trypsin inhibitor, (6) benzene, (7) toluene, (8) ethylbenzene, (9) propylbenzene, (10) butylbenzene, and (II) amylbenzene. [Reprinted from J. M. J. Frechet (1996). Pore-size specific modification as an approach to a separation media for single-column, two-dimensional HPLC, Am. Lab. 28, 18, p. 31. Copyright 1996 by International Scientific Communications, Inc.. Shelton, CT.]... 

Flow markers are often chosen to be chemically pure small molecules that can fully permeate the GPC packing and elute as a sharp peak at the total permeation volume (Vp) of the column. Examples of a few common flow markers reported in the literature for nonaqueous GPC include xylene, dioctyl phthalate, ethylbenzene, and sulfur. The flow marker must in no way perturb the chromatography of the analyte, either by coeluting with the analyte peak of interest or by influencing the retention of the analyte. In all cases it is essential that the flow marker experience no adsorption on the stationary phase of the column. The variability that occurs in a flow marker when it experiences differences in how it adsorbs to a column is more than sufficient to obscure the flow rate deviations that one is trying to monitor and correct for. 

Figure 2.21 A gas cluomatogram of a sample of river water (2.25 ml) spiked at 5 ppb levels with 1, toluene 2, ethylbenzene 3, methoxybenzene 4, p-dichlorobenzene 5, dimethylphe-nol 6, dimethylaniline 7, chloroaniline 8, indole 9, dichlorobenzonitrile 10, tiichlorophe-nol 11, dinitrobenzene 12, tiifluranil 13, atrazine 14, phenantlnene. Reprinted from Journal of High Resolution Chromatography, 16, H. G. J. Mol et al., Use of open-tubular tapping columns for on-line extraction-capillary gas cluomatography of aqueous samples , pp. 413-418, 1993, with permission from Wiley-VCH.

This multi-column swithching (GC-GC) technique has also been shown to be a powerful method for the separation of benzene and 1-methyl-cyclopentane in gasoline, as well as for the analysis of m-andp-xylenes in ethylbenzene. 

Figure 10-2. The Badger process for producing ethylbenzene (1) reactor, (2) fractionator (for recovery of unreacted benzene), (3) EB fractionator, (4) polyethylbenzene recovery column.

Benzene, toluene, ethylbenzene, p-xylene, m-xylene, oxylene 30 m CP CW57 CB column, 50-200° at 5°/min. 

GC assay of the organic layer showed no EIN(TMS)2 remaining after 15 min of stirring (GC conditions Restek RTX-1 column (30 m x 0.53 mm, 1 m film thickness), 2.53 mL/min, initial temperature 50°C, final temperature 300°C, rate 20 deg/min, injection temperature 200°C, detector temperature 350°C, injection volume 1 pL, inject sample neat retention times fert-butyl alcohol 1.4 min, THF 1.7 min, heptane 2.1 min, HN(TMS)2 2.6 min, ethylbenzene (present in commercial LHS) 3.1 min, te/ t-butyl acetate 4.0 min). Volume percents were determined based on standard solution counts. 

Figure 1.15 Fast analysis of a test mixture on a 10 cm x 4.6 mm I.D. column packed with 3 micrometer octa< ecylsilanized silica with a mobile phase flow rate of 3.4 mi. i.n (acetonitrile-water 7 3) and operating pressure of ca. 340 atmospheres. Peaks 1 uracil, 2 phenol, 3 - nitrobenzene, 4 - toluene, 5 -ethylbenzene, 6 - isopropylbenzene, and 7 - tert.-butylbenzene. (Reproduced with permission from ref. 222. Copyright Friedr. Vieweg 6 Sohn).

A column is to be designed to separate a mixture of ethylbenzene and styrene. The feed will contain 0.5 mol fraction styrene, and a styrene purity of 99.5 per cent is required, with a recovery of 85 per cent. Estimate the number of equilibrium stages required at a reflux ratio of 8. Maximum column bottom pressure 0.20 bar. 

The second column in the distillation train of an aromatics plant is required to split toluene and ethylbenzene. The recovery of toluene in the overheads must be 95%, and 90% of the ethylbenzene must be recovered in the bottoms. In addition to toluene and ethylbenzene, the feed also contains benzene and xylene. The feed enters the column under saturated conditions at a temperature of 170°C, with component flowrates given in Table 9.10. Estimate the mass balance around the column using the Fenske Equation. Assume that the K-values can be correlated by Equation 9.68 with constants A , 5 and C, given in Table 9.10. 

Fig. 11. Separation of a mixture of organic solvents using 50 cm long 100 (left) and 320 pm i.d. (right) monolithic capillary columns (Reprinted with permission from [112]. Copyright 2000 Wiley-VCH). Conditions temperature gradient 120 - 300 °C, 20 °C/min, inlet pressure 0.55 MPa, split injection. Peaks methanol (1), ethanol (2), acetonitrile (3), acetone (4), 1-propanol (5), methyl ethyl ketone (6), 1-butanol (7),toluene (8), ethylbenzene (9),propylbenzene (10),butyl-benzene (11)...

Figure 1.4 Different modes of chromatographs using the same column. Column, 5 pm Cj8-bonded silica gel, 15 cm x 4.6 mm i.d. Eluent A, tetrahydrofuran B, n-hexane C, acetonitrile flow rate, 0.5 ml min-1 at ambient detection, UV 260 nm. Peak 1, benzene, 2, ethylbenzene, 3, butylbenzene 4, octylbenzene and 5, polystyrene.

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